Basic Principles and Influencing Factors of Biological Phosphorus Removal

6.
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2.
1 Basic principles

There are a variety of processes used in wastewater treatment.
In recent years, the general development trend of phosphorus removal technology is chemical precipitation and phosphorus removal, especially the application of pre- and post-chemical precipitation is gradually decreasing, while the application of biological phosphorus removal technology is rapidly increasing
.

The promotion of biological phosphorus removal technology is attributed to its many advantages: saving chemicals; hydrolysis, acidification and gasification in the anaerobic stage (generating CH ₄ , CO ₂ and H ₂ in the anaerobic stage ), which can reduce the sludge output And has good dehydration performance, no need to digest, for this reason, the sludge digestion tank can be eliminated; the fertilizer value of biological phosphorus removal sludge is high

The mechanism of biological phosphorus removal has not been thoroughly studied yet
.

It is generally believed that under anaerobic conditions, facultative bacteria convert soluble BOD ₅ into low-molecular volatile organic acids (VFA)

(1) Phosphorus-accumulating bacteria take up phosphorus

C ₂ H _.
4 O ₂ + NH2 _.
4 ⁺ + O ₂ + PO _.
4 ^3- → C _.
5 H _.
7 NO ₂ + CO.
'S ₂ + (HPO _.
3 ) (polyphosphazene) + OH ^- + H ₂ O

(2) Phosphorus-accumulating bacteria release phosphorus

C ₂ H ₄ O ₂ +(HPO ₃ )(Polyphosphorus)+H ₂ O→(C ₂ H ₄ O ₂ ) ₂ (stored organic matter)+PO ₄ ^3- +3H ⁺

Figure 6-1 Principle of Biological Phosphorus Removal

Whether it is a continuous flow or batch batch biological phosphorus removal process, its effluent is difficult to meet increasingly stringent discharge standards.

For example, the total phosphorus discharge standard currently implemented in China is 0.

6.
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2.
2 Influencing factors of biological phosphorus removal

(1) The alternate introduction of anaerobic/aerobic conditions strengthens the superior selection of phosphorous accumulating bacteria.
As a result, a considerable part of the microorganisms are composed of such bacteria
.

(2) The denitrification of nitrate and easily degradable organic matter Nitrate reduces the easily degradable organic matter that should be stored in the cells of the phosphorus accumulating bacteria, resulting in weakening of the phosphorus uptake of the phosphorus accumulating bacteria; at the same time , the presence of nitrate inhibits the anaphora Oxygen releases phosphorus, which in turn affects the storage of easily degradable organic matter and phosphorus absorption in the aerobic section, resulting in reduced phosphorus removal effects
.

(3) The biological phosphorus removal effect of sludge age depends on the amount of surplus sludge removed.
Generally, the system with short sludge age produces more surplus sludge, and the phosphorus removal effect is better
.

(4) Both temperature and pH value are 10～30℃, can achieve better phosphorus removal effect; the suitable pH value range is 6～8
.

(5) BOD ₅ /TP It is generally believed that the higher BOD ₅ /TP has a better phosphorus removal effect, and the lower limit for biological phosphorus removal is BOD ₅ /TP=20
.

The difference in organic matter also has an impact on the phosphorus removal effect: easily degradable low-molecular-weight organic matter has a stronger ability to induce phosphorus release, and high-molecular-weight organic matter has a weaker ability to induce phosphorus release.

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